To speed production of work pieces, such as parts for assembling machines, it is efficient to use a retract clamp to hold the parts down while some forming operation is performed on the parts by a fixture such as a mill or drill press. One such retract clamp is shown in U.S. Pat. No. 5,752,693, (currently application No. 08/705,957) which is hereby fuilly incorporated herein by reference.
One problem encountered with retract clamps in general is inconsistent retraction. Not infrequently, the clamp arm will fail to retract frilly. This is generally caused by the arm or some component of the retract clamp becoming caught in the body of the clamp. When the clamp arm fails to fully retract, it can interfere with the proper removal and placement of work pieces. It can also interfere with the proper operation of the fixture. In either case, the production operation is halted, the work piece likely ruined, and the fixture can be damaged in some significant way.
Another problem encountered with retract clamps is seal failure. In a hydraulic retract clamp, a piston member is provided with a seal to contain hydraulic fluid in a hydraulic chamber. During normal operation, the piston member can tilt. When the piston member tilts, it pinches the seal. Over time the seal fails allowing hydraulic fluid to leak out of the hydraulic chamber eventually rendering the clamp inoperable.
The retract direction of the clamp arm in retract clamps is also generally problematic. If the retract clamp pulls the clamp arm rearwardly before the clamp arm moves upwardly and disengages the work piece, the clamp arm drags across the work piece which can leave marks on the work piece. Further, the clamp arm can move the work piece as it retracts. This moves the work piece out of position which can require that the production operation be halted.